Method for preparing monolayer carbon nanotube

ABSTRACT

A combination of a metal-based catalyst having a function as a catalyst for formation of graphite and a single-crystal substrate having a certain correspondence to the metal-based catalyst with respect to the crystal grain size and the crystal orientation thereof is used; the metal-based catalyst is dispersed on the single-crystal substrate; and a carbon material is fed to the substrate at any temperature not lower than 500° C. to thereby form single single-walled carbon nanotubes through vapor phase thermal decomposition growth on the substrate. More precisely, the invention of this application enables production of single-walled carbon nanotubes with controlled diameter, requiring neither a porous material nor catalyst particles for use as a catalyst carrier. One example of the combination of the metal-based catalyst and the single-crystal substrate is a combination of Fe and sapphire substrate.

TECHNICAL FIELD

The invention of this application relates to a method for producingsingle-walled carbon nanotubes. More precisely, the invention of thisapplication relates to a method for producing single-walled carbonnanotubes, which do not require a porous material or catalyst particlesas a catalyst carrier and which enable production of single-walledcarbon nanotubes with controlled diameter.

BACKGROUND ART

Heretofore, chemical vapor deposition (CVD) methods have beenspecifically given attention in production of high-quality single-walledcarbon nanotubes (SWNTs), that are extremely useful in variousindustries. This is because CVD methods may enable industrialmass-production of SWNTs and have the potential for controlling thevapor phase thermal decomposition growth of SWNTs by skillfullycontrolling the type and the particle size of the catalyst to be used.

Many researchers have made various studies relating to the production ofSWNTs through chemical vapor deposition, and some reports have been madeby them. For example, J. King. et al. have reported that SWNTs can beobtained by heating to 1000° C. a substrate coated with a mixture ofFe(NO₃)₃.9H₂O, Mo(acac)₂ and alumina nanoparticles in a methane gasatmosphere. J. H. Hafner, et al. have reported that SWNTs grow whennanometer-size metal particles supported on alumina nanoparticles areheated with circulated CO gas. In these experiments, a salt of Fe and/orMo is used as a metal-based catalyst, and alumina nanoparticles are usedas the carrier.

There are other reports of production of SWNTs through chemical vapordeposition, reporting that use of porous material such as zeolite,silica or anodized silicon oxide as a carrier enables production ofSWNTs.

However, it is to be noted that, when chemical vapor deposition iscarried out without use of such nanoparticles or porous material as acarrier in the above-mentioned experiments, then SWNTs could not beformed but only multi-walled carbon nanotubes are obtained irrespectiveof the amount and the size of the metal-based catalyst used.

Specifically, in production of SWNTs through conventional vapor phasedeposition, use of a metal-based catalyst and nanoparticles or porousmaterial as a carrier of the metal-based catalyst is an indispensablerequirement. Taking industrial mass-production of SWNTs intoconsideration, a substrate that has a fine structure comparable to thatof nanoparticles or porous material and has a broad surface area will beneeded as the carrier.

The invention of this application has been made in consideration of theabove-mentioned situation, and its object is to provide a method forproducing single-walled carbon nanotubes, which does not requirenanoparticles and porous material as a carrier and which enablesproduction of single-walled carbon nanotubes with controlled diameter.

DISCLOSURE OF THE INVENTION

To solve the above-mentioned problems, the invention of this applicationprovides the following:

In the first aspect thereof, the invention provides a method forproducing single-walled carbon nanotubes, which comprises using acombination of a metal-based catalyst having a catalytic function information of graphite and a single-crystal substrate having a certaincorrespondence to the metal-based catalyst with respect to the crystalgrain size and the crystal orientation thereof, dispersing themetal-based catalyst on the single-crystal substrate, and feeding acarbon material to the substrate at any temperature not lower than 500°C. to thereby grow single-walled carbon nanotubes through vapor phasethermal decomposition.

In the second aspect thereof, the invention provides a method forproducing single-walled carbon nanotubes, wherein the single-crystalsubstrate is coated with a thin film of metal-based catalyst; in thethird aspect thereof, the invention provides a method for producingsingle-walled carbon nanotubes, wherein the thin film of metal-basedcatalyst has a thickness of from 0.1 to 10 nm; in the fourth aspectthereof, the invention provides a method for producing single-walledcarbon nanotubes, wherein the metal-based catalyst is any one or amixture of elements of a group consisting of iron group metals, platinumgroup metals, rare earth metals, transition metals, and their metalcompounds; in the fifth aspect thereof, the invention provides a methodfor producing single-walled carbon nanotubes, wherein the single-crystalsubstrate is formed of a substance stable at 500° C. or higher; in thesixth aspect thereof, the invention provides a method for producingsingle-walled carbon nanotubes, wherein the single-crystal substrate issapphire (Al₂O₃), silicon (Si), SiO₂, SiC, or MgO; in the seventh aspectthereof, the invention provides a method for producing single-walledcarbon nanotubes, wherein hydroxyapatite is used in place of thesingle-crystal substrate; in the eighth aspect thereof, the inventionprovides a method for producing single-walled carbon nanotubes, whereinsingle-walled carbon nanotubes with controlled diameter are grownthrough vapor phase thermal decomposition, the diameter depending on thecombination of the metal-based catalyst, the single-crystal substrate,and the crystal plane where the two contact; in the ninth aspectthereof, the invention provides a method for producing single-walledcarbon nanotubes, wherein the combination of the metal-based catalyst,the single-crystal substrate, and the crystal plane where the twocontact is a combination of Fe and the A-plane, R-plane or C-plane ofsapphire; in the tenth aspect thereof, the invention provides a methodfor producing single-walled carbon nanotubes, wherein the carbonmaterial is a carbon-containing substance that is gaseous at anytemperature not lower than 500° C.; in the eleventh aspect thereof, theinvention provides a method for producing single-walled carbonnanotubes, wherein the carbon material is methane, ethylene,phenanthrene, or benzene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 includes photographs of SEM images, showing a deposit grown at800° C. on the A-plane (a), the R-plane (b) and the C-plane (c) ofsapphire coated with a thin Fe film having a thickness of 2 nm.

FIG. 2 includes photographs of SEM images, showing a deposit grown at800° C. on the A-plane (a), the R-plane (b) and the C-plane (c) ofsapphire coated with a thin Fe film having a thickness of 5 nm.

FIG. 3 includes photographs of TEM images, showing a deposit grown on(a) A (2 nm), (b) R (2 nm), and (c) C (5 nm).

FIG. 4 shows the Raman scattering spectrum of single-walled carbonnanotubes produced in Example; (a) indicate a range of up to 500 cm⁻¹,and (b) indicates a range of from 1200 to 1800 cm⁻¹.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention of this application has the characteristics as above, andits embodiments are described hereinunder.

The method for producing single-walled carbon nanotubes of the inventionof this application comprises using a combination of a metal-basedcatalyst that has a catalytic function in the formation of graphite, anda single-crystal substrate that has a certain correspondence to themetal-based catalyst with respect to the crystal grain size and thecrystal orientation thereof, dispersing the metal-based catalyst on thesingle-crystal substrate, and feeding a carbon material to the substrateat any temperature not lower than 500° C. to thereby grow single-walledcarbon nanotubes through vapor phase thermal decomposition.

In the invention of this application, various types of metals having acatalytic function in formation of graphite, that is, in vapor phasethermal decomposition growth of single-walled carbon nanotubes, may beused for the metal-based catalyst. Concretely, for example, any one or amixture of components of the group consisting of iron group metals suchas Ni, Fe, Co; platinum group metals such as Pd, Pt, Rh; rare earthmetals such as La, Y; transition metals such as Mo, Mn; and their metalcompounds may be used herein.

For the single-crystal substrate, any of various materials that arestable at the treatment temperature of 500° C. or higher can be used.For example, they include sapphire (Al₂O₃), silicon (Si), SiO₂, SiC, andMgO. In contrast to those in the related art, these materials are notalways required to be porous structures or nanoparticles, and they maybe flat. In the invention of this application, the single-crystalsubstrate may be replaced, for example by pillar crystals such ashydroxyapatite.

One characteristic feature of the invention of this application residesin the combination of the metal-based catalyst and the single-crystalsubstrate. In the invention of this application, the metal-basedcatalyst and the single-crystal substrate have a specific correspondenceto each other. Specifically, the metal-based catalyst may be combinedwith the single-crystal substrate in such a manner that the substratemay act on the specific correspondence to the catalyst in point of thecrystal grain size of the recrystallized grains thereof formed throughsolid-phase reaction such as deposition or recrystallization of themetal-based catalyst at the treatment temperature of 500° C. or higher,and of the crystal orientation between the neighboringnon-recrystallized grains. More concretely, for example, it is desirablethat the single-crystal substrate may control the crystal grain size ofthe metal-based catalyst to fall within a range of from 0.1 to 10 nm orso, at the treatment temperature of 500° C. or higher, and may have arelation with the metal-based catalyst which acts to make the crystalplane of the catalyst specifically oriented relative to thesingle-crystal substrate. One preferred embodiment of the combination ofthe metal-based catalyst and the single-crystal substrate in theinvention of this application is a combination of Fe and sapphire.

The mode of dispersing the metal-based catalyst on the single-crystalsubstrate is not specifically defined. For example, it may be realizedby dispersing fine particles of a metal-based catalyst on asingle-crystal substrate, or by coating a single-crystal substrate witha thin film of a metal-based catalyst. The latter method is preferred,as it is simple in actual production lines. Various methods may beutilized for the dispersion, concretely including, for example, a dryprocess of vacuum evaporation or sputtering, and a wet process ofliquid-dropping, spraying or spin-coating.

The amount of the metal-based catalyst to be dispersed on thesingle-crystal substrate is not specifically defined, and may be anydesired one. For example, the catalyst may be partially or whollydispersed on the single-crystal substrate to a thickness of one atomiclayer or so. When it is desired that the single-walled carbon nanotubesare obtained at a relatively high yield, then for example a metal-basedcatalyst is dispersed on a single-crystal substrate as a thin filmthereof and the thickness of the film is controlled to fall within arange of from 0.1 to 10 nm or so, though this may not always bedesirable depending on the combination of the metal-based catalyst andthe single-crystal substrate. If the film of metal-based crystal is toothick, then it is unfavorable since the film may not be able to interactwith the single-crystal substrate locally in some surface part thereofand, as a result, there may be a possibility that the metal-basedcatalyst particles cannot be controlled by the substrate.

The single-crystal substrate thus having the metal-based catalystdispersed thereon is heated at any temperature not lower than 500° C.,and then a carbon material is fed to it.

Heating the single-crystal substrate to any temperature not lower than500° C. may be done in an inert atmosphere. The carbon material may beany of the carbon-containing substances that are gaseous at anytemperature not lower than 500° C. More concretely, it includes, forexample, methane (CH₄), ethylene (C₂H₄), carbon monoxide (CO) and othersthat are gaseous at room temperature; and phenanthrene, benzene andothers that are solid or liquid at room temperature but become gaseouswhen heated at 500° C. or higher. With it, single-walled carbonnanotubes may be grown on the surface of the single-crystal substratethrough vapor phase thermal decomposition thereon.

When the metal-based catalyst and the single-crystal substrate aresuitably combined in the manner as above, then single-walled carbonnanotubes may be produced, not requiring porous-structured orgranular-shaped single-crystal substrates as in the related art.

Having noted the interaction between the metal-based catalyst and thesingle-crystal substrate in the invention of this application, we, thepresent inventors have made more detailed studies into this, and as aresult have found that not only the combination of the metal-basedcatalyst and the single-crystal substrate as above but also the crystalplane of the single-crystal substrate should be taken into considerationin determining the interaction between the metal-based catalyst and thesingle-crystal substrate, and that the diameter of the single-walledcarbon nanotubes to be formed may be specifically controlled dependingon the combination of all the above. The technology of controlling thediameter of single-walled carbon nanotubes in producing them in a modeof vapor phase thermal decomposition growth thereof has not been knownat all up to now, and we, the present inventors, are the first to haverealized it. Specifically, the method for producing single-walled carbonnanotubes which the invention of this application provides herein ischaracterized in that the specific combination of the metal-basedcatalyst, the single-crystal substrate, and its crystal plane connectingthe two realizes vapor phase thermal decomposition growth ofsingle-walled carbon nanotubes with a specific diameter.

More concretely, for example, for the preferred combination ofmetal-based catalyst and single-crystal substrate, Fe and sapphirementioned above, the combination of Fe with any of the A-plane, R-planeor C-plane of sapphire may be taken into consideration, and the diameterof the single-walled carbon nanotubes to be formed through vapor phasethermal decomposition growth thereof may be controlled differently inevery combination of these. For example, regarding the combination of Fewith the A-plane, R-plane or C-plane of sapphire, the diameter of thesingle-walled carbon nanotubes to be grown is controlled to specificvalues of 1.43 nm, 1.30 nm and 1.20 nm on the A-plane; 1.45 μm, 1.24 nmand 1.18 nm on the R-plane; and 1.49 nm, 1.31 nm and 1.18 μm on theC-plane.

In the invention of this application, in addition, the thickness of thethin film of metal-based catalyst may be controlled differently on eachcrystal plane of the single-crystal substrate and the yield of thesingle-walled carbon nanotubes to be produced may be thereby increased.More concretely, for example, regarding the combination of Fe with anyof the A-plane, R-plane or C-plane of sapphire, the yield of thesingle-walled carbon nanotubes may be increased on the A-plane and theR-plane by reducing the thickness of the thin Fe film thereon within therange mentioned above, while the yield thereof to be formed on theC-plane may be increased by increasing the thickness of the thin Fe filmthereon within that range.

On the other hand, existence of single-walled carbon nanotubes ofvarious symmetry (chirality) is known. The chirality of single-walledcarbon nanotubes may be represented by chirality indexes (m, n), and ithas strong correlation with the diameter of the single-walled carbonnanotubes. This suggests the possibility that the method of theinvention of this application may control not only the diameter but alsothe chirality of single-walled carbon nanotubes.

As described hereinabove, the invention of this application indicatesthat the interaction between the metal-based catalyst and thesingle-crystal substrate material plays an important part in vapor phasethermal decomposition growth of single-walled carbon nanotubes, and,when a single-crystal substrate with such a metal-based catalystdispersed thereon is used, then single-walled carbon nanotubes may begrown through vapor phase thermal decomposition thereon. In addition,when the combination of the metal-based catalyst with the single-crystalsubstrate and its crystal plane is suitably selected, the diameter ofthe single-walled carbon nanotubes is controlled. Further, when thecrystal plane of the single-crystal substrate and the thickness of thethin catalyst layer formed thereon are suitably controlled, then theyield of the single-walled carbon nanotubes to be formed on thesubstrate may be increased.

Example of the invention is described below with reference to thedrawings attached hereto, and the embodiments of the invention aredescribed in more detail.

EXAMPLE

Producing SWNTs was tried, using a tube furnace having an inner diameterof 2 inches and using methane gas as the carbon material. For thesingle-crystal substrate, the A-plane, R-plane and C-plane of sapphirewere used. On the single-crystal substrate, a thin Fe film serving asthe metal-based catalyst was formed through electron beam deposition ina vacuum of about 4×10⁻⁶ Torr so that its thickness would be from 2 to 5nm.

These substrates were introduced into a tube furnace and heated in anargon atmosphere; and after they reached a predetermined temperaturebetween 600° C. and 800° C., methane (99.999%) used here as the carbonmaterial was fed thereinto at a flow rate of 0.6 liters/min. The methaneintroduction continued for 5 minutes, and then argon was againintroduced into the furnace. Then, the tube furnace was cooled to roomtemperature.

After the heat treatment, the substrates were analyzed in detail throughobservation with a scanning electron microscope (SEM), through Ramanspectrometry and through observation with a transmission electronicmicroscope (TEM). The samples for SEM observation were coated each witha thin Pd-Pt film having a thickness of about 2 nm for more definiteobservation thereof. For Raman spectrometry, the samples were exposed to488 nm light (30 mW) from an Ar laser having a convergent spot size ofabout 1 μm. The samples for TEM observation were prepared by collectingthe deposit from the sapphire substrate, dispersing it in ethanol,dropwise applying the resulting dispersion onto a TEM grid and drying itthereon.

SEM Observation

FIG. 1(a)(b)(c) show SEM images of the deposit grown at 800° C. on theA-plane, R-plane and C-plane, respectively, of sapphire coated with athin Fe film having a thickness of 2 nm. It is definitely observed thatthe amount of the tubular deposit on the A-plane is larger than that onthe R-plane. In addition, it is also clear that the amount of the tubedeposit on the C-plane is the smallest of the three.

FIG. 2(a)(b)(c) show SEM images of the deposit grown at 800° C. on theA-plane, R-plane and C-plane, respectively, of sapphire coated with athin Fe film having a thickness of 5 nm. It is confirmed that the sametubular deposit as in the above is formed on all the three planes. It isunderstood that these nanotubes are either thick and short ones (havinga diameter of from 20 to 50 nm and a length of about 1 mm), or thin andlong ones (having a diameter of less than 3 nm and a length of 2 mm ormore).

In addition, when the sapphire coated with a thin Fe film having athickness of 2 nm was heated at 600° C., then hardly any tubulardeposits grew on the A-plane and the R-plane of the substrate, but a fewthicker nanotubes (having a diameter of from about 30 to 50 nm) werefound to have grown on the C-plane. The structure of these nanotubes wasanalyzed through TEM observation and Raman spectrometry thereof.

TEM Observation

FIG. 3(a) shows a TEM image of the deposit grown on the A-plane ofsapphire coated with a thin Fe film having a thickness of 2 nm (this ishereinafter indicated by A (2 nm)). It is understood that A (2 nm)includes SWNTs and an extremely small amount of amorphous carbon (thisis hereinafter indicated by a-C). The TEM image of the deposit grown onthe R-plane of sapphire coated with a thin Fe film having a thickness of2 nm (this is hereinafter indicated by R (2 nm)), shown in FIG. 3(b),confirms that R (2 nm) includes SWNTs and a-C. The TEM image of thedeposit grown on the C-plane of sapphire coated with a thin Fe filmhaving a thickness of 5 nm (this is hereinafter indicated by C (5 nm)),shown in FIG. 3(c), confirms that the amount of a-C is the largest on C(5 nm) and there are hardly any SWNTs. Though not shown in FIG. 3(c), itis confirmed that on C (5 nm) some double-walled carbon nanotubes weregrown.

The TEM observation confirms that the diameter of SWNTs bundled on theA-plane, R-plane and C-plane of the substrate falls approximatelybetween 1.0 and 1.7 nm.

Raman Spectrometry

FIG. 4(a)(b) show the Raman scattering spectrum of the deposit formed onthe A-plane, R-plane and C-plane of sapphire coated with a thin Fe filmhaving a thickness of 2 nm, 3 nm or 5 nm. All the samples showed peaksat about 1592 cm⁻¹ and 1570 cm⁻¹, and showed from 1 to 4 fine peakswithin a range of from 100 to 230 cm⁻¹. These peaks are characteristicsof SWNTs, and indicate the presence of SWNTs in the deposit. The peaksappearing at about 1592 cm⁻¹ and 1570 cm⁻¹ correspond to the tangentmode, and the peaks appearing between 100 and 230 cm⁻¹ correspond toRaman bleeding mode (RBM) of the SWNTs.

For example, SWNTs formed on R (2 nm) gave a strong RBM peak at 167 cm⁻¹indicating that these are SWNTs having a diameter of 1.4 nm, and gave aweak peak at 203 cm⁻¹ indicating that these are SWNTs having a diameterof 1.2 nm. However, it was found that the peaks given by the samplescoated with an Fe film thicker than this are not pronounced. Thus, it isconcluded from the tangent mode and RBM mode peak intensity data that,with the increase in the thickness of the Fe film from 2 nm to 5 nm, theamount of SWNTs formed on the A-plane and the R-plane decreases. On theother hand, however, it is found that the amount of SWNTs formed on theC-plane increases with the increase in the thickness of the Fe film from2 nm to 5 nm.

The peak position and the RBM intensity of these SWNTs differ amongindividual deposits thereof at different positions. Each deposit wasmore carefully analyzed in at least 10 different points thereof, and, asa result, the following tendency was clear. Specifically, the RBM peakwidth is narrow, falling between 7 and 12 cm⁻¹; the number of the peaksis from 1 to 4; and the peak position depends on the plane of thesubstrate sapphire.

More concretely, for example, the Raman spectra obtained at 10 sites onthe A-plane (2 nm), the R-plane (2 nm) and the C-plane (2 nm) wereseparately averaged, and the RBM peak and the calculated diameter ofSWNTs are shown in Table 1. TABLE 1 RBM Peak (cm⁻¹) Sample SWNTsdiameter (nm) A (2 nm) 170 188 203 1.43 1.30 1.20 R (2 nm) 168 194 2071.45 1.24 1.18 C (2 nm) 164 186 206 1.49 1.31 1.18

As in the above, when the crystal plane of the sapphire substrate isspecifically selected, then SWNTs can be formed thereon with theirdiameter controlled to be a specific value.

Comparative Example 1

In place of the substrate sapphire in the above-mentioned Example, asilicon single-crystal plane (or SiO₂ plane thermally grown on silicon)was used, but SWNTs could not be formed thereon through CVD at 800° C.irrespective of the thickness of the thin Fe film formed thereon.

Comparative Example 2

A sapphire substrate was coated with a thin Ni film in place of the thinFe film as in the above-mentioned Example, and then processed in thesame manner as above. However, SWNTs could not be formed on it.

Comparative Example 3

A silicon wafer with a mixture of Fe(NO₃)₃.H₂O and alumina nanoparticles(with no Mo(acac)₂) applied thereto was prepared as a substrate. Thiswas subjected to the same heat treatment as in the above-mentionedExample, and SWNTs were formed on it. The Raman spectrum of these SWNTsis shown in FIG. 4. The RBM peak of the Raman spectrum is broad, fallingbetween 120 and 200 cm⁻¹, and this means that the diameter of SWNTsformed herein varies to fall within a broad range of from 1.2 to 2.0 nm.

From this, it is understood that, though the alumina nanoparticles ofthe metal-based catalyst carrier are formed of Al₂O₃, the same as thatof sapphire, the alumina nanoparticles have various crystal planes andamorphous characteristics because of their morphology, and therefore,SWNTs could grow thereon but the diameter of SWNTs grown thereon couldnot be controlled, and, as a result, the diameter of SWNTs grown thereonfell within a broad range.

Because of the reasons above, the production of SWNTs in conventionalvapor phase thermal decomposition growth on a catalyst carrierunavoidably requires a porous material and nanoparticles as the catalystcarrier. In the invention of this application, however, when the crystalto be the substrate, the crystal plane of the substrate, the metal-basedcatalyst, the film thickness of the catalyst and the crystal growingtemperature are suitably selected, then SWNTs may be formed even on aflat crystal substrate. Accordingly, it is surmised that theserequirements stipulated by the invention have influence on the catalystmetal diffusion coefficient and on the crystal grain size and thecrystal orientation of the catalyst metal incidental to it, and, as aresult, SWNTs having a specific diameter may be formed on the substrate.

Needless-to-say, the invention is not limited to the embodimentsdescribed hereinabove, and its details may undergo various changes andmodifications.

INDUSTRIAL APPLICABILITY

As described in detail hereinabove, the invention relates to a methodfor producing single-walled carbon nanotubes. More precisely, theinvention of this application provides a method for producingsingle-walled carbon nanotubes, which does not require a porous materialand catalyst particles and which enables production of single-walledcarbon nanotubes with controlled diameter.

1. A method for producing single-walled carbon nanotubes, which comprises using a combination of a metal-based catalyst having a function as a catalyst for formation of graphite, and a single-crystal substrate having a certain correspondence to the metal-based catalyst with respect to the crystal grain size and the crystal orientation thereof, dispersing the metal-based catalyst on the single-crystal substrate, and feeding a carbon material to the substrate at any temperature not lower than 500° C. to thereby grow single-walled carbon nanotubes through vapor phase thermal decomposition.
 2. The method for producing single-walled carbon nanotubes as claimed in claim 1, wherein the single-crystal substrate is coated with a thin film of metal-based catalyst.
 3. The method for producing single-walled carbon nanotubes as claimed in claim 1, wherein the thin film of metal-based catalyst has a thickness of from 0.1 to 10 nm.
 4. The method for producing single-walled carbon nanotubes as claimed in claim 1, wherein the metal-based catalyst is any one or a mixture of two or more components of the group consisting of iron group metals, platinum group metals, rare earth metals, transition metals and their metal compounds.
 5. The method for producing single-walled carbon nanotubes as claimed in claim 1, wherein the single-crystal substrate is formed of a substance stable at 500° C. or higher.
 6. The method for producing single-walled carbon nanotubes as claimed in claim 5, wherein the single-crystal substrate is any of sapphire (Al₂O₃), silicon (Si), SiO₂, SiC or MgO.
 7. The method for producing single-walled carbon nanotubes as claimed in claim 1, wherein hydroxyapatite is used in place of the single-crystal substrate.
 8. The method for producing single-walled carbon nanotubes as claimed in claim 1, wherein single-walled carbon nanotubes with controlled diameter are grown through vapor phase thermal decomposition, the diameter depending on the combination of the metal-based catalyst and the single-crystal substrate and its crystal plane.
 9. The method for producing single-walled carbon nanotubes as claimed in claim 8, wherein the combination of the metal-based catalyst, the single-crystal substrate and the crystal plane connecting the two is a combination of Fe and any of A-plane, R-plane or C-plane of sapphire.
 10. The method for producing single-walled carbon nanotubes as claimed in claim 1, wherein the carbon material is a carbon-containing substance that is gaseous at any temperature not lower than 500° C.
 11. The method for producing single-walled carbon nanotubes as claimed in claim 10, wherein the carbon material is methane, ethylene, phenanthrene or benzene. 